JP2007126544A - Water-based ink for inkjet recording - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide water-based ink for inkjet recording, excellent in scratch resistance when printing it on exclusive paper such as photographic paper and realizing high printing density when printing it on plain paper. <P>SOLUTION: The water-based ink for inkjet recording comprises yellow pigment dispersed particles. In the water base ink, the number of dispersed yellow pigment particles with a diameter of ≥0.57 μm among the yellow pigment dispersed particles containing ≥4.5 wt.% yellow pigment is ≤1.2×10<SP>7</SP>particles/mL. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an aqueous ink for inkjet recording.

The ink jet recording system is a recording system in which characters and images are obtained by ejecting ink droplets directly from a very fine nozzle and attaching them to a recording member. This method is easy to make full color and is inexpensive, and has a widespread use because it has many advantages such as the ability to use plain paper as a recording member and non-contact with the substrate.
Among them, in recent years, those using pigment-based ink as a colorant have become mainstream from the viewpoint of weather resistance and water resistance of printed matter (see, for example, Patent Document 1).

Patent Document 2 discloses that the number average particle diameter in a dispersed state is in the range of 10 to 100 nm for the purpose of improving storage stability and improving density unevenness during printing and fixability after printing. An inkjet recording ink containing a water-insoluble colorant, a water-soluble polymer dispersant having a specific solubility parameter, and the like is disclosed.
Furthermore, Patent Document 3 discloses a recording ink in which a pigment as a coloring material is dispersed in a solvent containing at least water in order to provide a low viscosity and high stability over time. An ink for recording, wherein the dispersed pigment has an average particle size of 0.05 to 0.1 μm and the particle size of almost all pigments is distributed within a range of 0.01 to 0.3 μm. It is disclosed.
However, the above water-based ink does not satisfy the high level of scratch resistance and print density required for recent photographic images.

International Publication No. 00/39226 Pamphlet JP-A-11-140356 JP 07-331147 A

  An object of the present invention is to provide a water-based ink for ink-jet recording which has excellent scratch resistance when printed on special paper such as photographic paper and has a high print density when printed on plain paper.

The present invention relates to a water-based ink containing a yellow pigment dispersion, which contains 4.5% by weight or more of the yellow pigment and has a particle diameter of 0.57 μm or more among the yellow pigment dispersion. Provided is an aqueous ink for inkjet recording in which the number of dispersions is 1.2 × 10 ⁷ / ml or less.

  ADVANTAGE OF THE INVENTION According to this invention, the aqueous ink for inkjet recordings which is excellent in abrasion resistance when printing on special papers, such as a photographic paper, and has a high printing density when printing on plain paper can be obtained.

[Yellow pigment]
Examples of yellow pigments used in the present invention (hereinafter sometimes simply referred to as “pigments”) include yellow pigments such as azo lake pigments, insoluble azo pigments, condensed azo pigments, polycyclic pigments, and metal complex pigments. Can be mentioned.
Examples of azo lake pigments include acetoacetyl allylide pigments, and more specifically, C.I. I. Pigment yellow 133, 168, 169 and the like.
Examples of insoluble azo pigments include acetoacetate allylide monoazo pigments, acetoacetate allylide disazo pigments, and pyrazolone pigments.

Examples of the acetoacetyl allylide monoazo pigment include Hansa pigments and benzimidazolone pigments. Examples of Hansa pigments include C.I. I. Pigment Yellow 1, 2, 3, 5, 6, 49, 63, 65, 73, 74, 75, 87, 90, 97, 98, 106, 111, 114, 116, 121, 124, 126, 127, 130 136, 152, 165, 167, 170, 174, 176, 188 and the like. Examples of benzimidazolone pigments include C.I. I. Pigment yellow 120, 151, 154, 156, 175, 180, 181, 194 and the like.
Examples of acetoacetyl allylide disazo pigments include C.I. I. Pigment yellow 12, 13, 14, 17, 55, 81, 83, 113, 171, 172 and the like.
Examples of pyrazolone pigments include C.I. I. Pigment yellow 10, 60 and the like.

Examples of condensed azo pigments include C.I. I. Pigment yellow 93, 94, 95, 128, 166 and the like.
Examples of polycyclic pigments include isoindolinone pigments, flavanthrone pigments, and quinophthalone pigments. Examples of isoindolinone pigments include C.I. I. Pigment yellow 109, 110, 173, etc. I. Pigment Yellow 24 and the like, and quinophthalone pigments include C.I. I. And CI Pigment Yellow 138.
Examples of the metal complex pigment include C.I. I. Pigment yellow 117, 129, 150, 153, 177, 179, 257, 271 and the like.
In addition, C.I. I. Pigment Yellow 139, 185 and the like, isoindoline pigments such as C.I. I. Anthraquinone pigments such as CI Pigment Yellow 99, 108, 123, 147, 193, and 199 can be used.
The above pigments can be used alone or in combination of two or more.

  Among these pigments, insoluble azo pigments such as Hansa pigments and benzimidazolone pigments; polycyclic pigments such as condensed azo pigments and isoindolinone pigments are preferable. I. One or more pigments selected from the group consisting of CI Pigment Yellow 74, 93, 97, 110, 128 and 151 are more preferable, and C.I. I. Pigment yellow 74 and C.I. I. It is preferably at least one selected from the group consisting of CI Pigment Yellow 97.

  The average primary particle diameter of the pigment is preferably 10 to 200 nm, more preferably 15 to 180 nm, and still more preferably 20 to 150 nm, from the viewpoint of pigment dispersibility, printing density, and scratch resistance. The average primary particle diameter of the pigment can be measured using a transmission electron microscope. For example, the number average particle diameter obtained by calculating 500 averages by image analysis of a transmission electron microscope of JEOL Ltd. is used. Can do. In addition, when a pigment has a major axis and a minor axis, the major axis is used for calculation.

[Yellow pigment dispersion]
The yellow pigment dispersion in the present invention includes (i) a yellow pigment dispersion contained in water-insoluble polymer particles, that is, a dispersion of water-insoluble polymer particles containing a yellow pigment, or (ii) dispersed in a water-soluble polymer. A yellow pigment dispersion. These dispersions are described below.

(I) A dispersion of water-insoluble polymer particles containing a yellow pigment
A water-insoluble polymer is used as the polymer constituting the polymer particles containing the water-insoluble polymer yellow pigment in order to easily contain the pigment. Here, the water-insoluble polymer refers to a polymer having a dissolution amount of less than 1 g when the polymer is dried at 105 ° C. for 2 hours and then dissolved in 100 g of water at 25 ° C. When the polymer has a salt-forming group, the dissolution amount is a dissolution amount when the salt-forming group of the polymer is 100% neutralized with acetic acid, sodium hydroxide or the like according to the type.
Examples of water-insoluble polymers include water-insoluble vinyl polymers, water-insoluble ester polymers, water-insoluble urethane polymers, and the like. Among these, a water-insoluble vinyl polymer is preferable from the viewpoint of dispersion stability of the aqueous dispersion.
The water-insoluble vinyl polymer is a polymer obtained by addition polymerization of vinyl monomers such as vinyl compounds, vinylidene compounds, vinylene compounds.

  Examples of the water-insoluble vinyl polymer include (a) a salt-forming group-containing monomer (hereinafter sometimes referred to as “(a) component”), (b) a macromer (hereinafter sometimes referred to as “(b) component”) and / or (C) A water-insoluble vinyl polymer obtained by copolymerizing a monomer mixture (hereinafter sometimes simply referred to as “monomer mixture”) containing a hydrophobic monomer (hereinafter sometimes referred to as “component (c)”) is preferred. . This water-insoluble vinyl polymer has a structural unit derived from component (a), a structural unit derived from component (b) and / or a structural unit derived from component (c).

(A) The salt-forming group-containing monomer is used from the viewpoint of enhancing the dispersion stability of the resulting dispersion. Examples of the salt-forming group include a carboxy group, a sulfonic acid group, a phosphoric acid group, an amino group, and an ammonium group.
Examples of the salt-forming group-containing monomer include a cationic monomer and an anionic monomer. Examples thereof include those described in JP-A-9-286939, page 5, column 7, line 24 to column 8, line 29.
Representative examples of the cationic monomer include unsaturated amine-containing monomers and unsaturated ammonium salt-containing monomers. Among these, N, N-dimethylaminoethyl (meth) acrylate, N- (N ′, N′-dimethylaminopropyl) (meth) acrylamide and vinylpyrrolidone are preferable.

Representative examples of the anionic monomer include unsaturated carboxylic acid monomers, unsaturated sulfonic acid monomers, unsaturated phosphoric acid monomers, and the like.
Examples of the unsaturated carboxylic acid monomer include acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, and 2-methacryloyloxymethyl succinic acid. Examples of the unsaturated sulfonic acid monomer include styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, 3-sulfopropyl (meth) acrylate, bis- (3-sulfopropyl) -itaconic acid ester, and the like. Examples of unsaturated phosphoric acid monomers include vinylphosphonic acid, vinyl phosphate, bis (methacryloxyethyl) phosphate, diphenyl-2-acryloyloxyethyl phosphate, diphenyl-2-methacryloyloxyethyl phosphate, dibutyl-2-acryloyloxy Examples thereof include ethyl phosphate.
Among the anionic monomers, from the viewpoint of dispersion stability, unsaturated carboxylic acid monomers are preferable, and acrylic acid and methacrylic acid are more preferable.

  The (b) macromer is used from the viewpoint of improving the dispersion stability, scratch resistance, etc. of the polymer particles, particularly when the polymer particles contain a pigment. The macromer includes a macromer which is a monomer having a polymerizable unsaturated group having a number average molecular weight of preferably 500 to 100,000, more preferably 1,000 to 10,000. In addition, the number average molecular weight of (b) macromer can be measured using a polystyrene as a standard substance by a gel chromatography method using 1 mmol / L dodecyldimethylamine-containing chloroform as a solvent.

As the (b) macromer, from the viewpoint of dispersion stability of polymer particles, scratch resistance, etc., a styrene macromer and an aromatic group-containing (meth) acrylate macromer having a polymerizable functional group at one end are preferable.
Examples of the styrenic macromer include a styrene monomer homopolymer or a copolymer of a styrene monomer and another monomer. Examples of the styrene monomer (b-1) include styrene, 2-methylstyrene, vinyl toluene, ethyl vinyl benzene, vinyl naphthalene, chlorostyrene, and the like.

  Examples of the aromatic group-containing (meth) acrylate-based macromer include a homopolymer of an aromatic group-containing (meth) acrylate or a copolymer thereof with another monomer. The aromatic group-containing (meth) acrylate (b-2) may have a substituent containing a hetero atom, and has 6 to 22 carbon atoms, preferably 6 to 18 carbon atoms, and more preferably 6 carbon atoms. An arylalkyl group having 12 to 12 carbon atoms, or an aryl group having 6 to 22 carbon atoms, preferably 6 to 18 carbon atoms, and more preferably 6 to 12 carbon atoms, which may have a substituent containing a hetero atom. (Meth) acrylate etc. are mentioned. Examples of the substituent containing a hetero atom include a halogen atom, an ester group, an ether group, and a hydroxy group. Examples of the aromatic group-containing (meth) acrylate (b-2) include benzyl (meth) acrylate, phenoxyethyl (meth) acrylate, 2-hydroxy-3-phenoxypropyl acrylate, 2-methacryloyloxyethyl-2- Examples thereof include hydroxypropyl phthalate, and benzyl (meth) acrylate is particularly preferable.

The polymerizable functional group present at one end of the macromer is preferably an acryloyloxy group or a methacryloyloxy group, and the other monomer to be copolymerized is preferably acrylonitrile.
The content of the styrene-based monomer (b-1) in the styrene-based macromer or the aromatic group-containing (meth) acrylate (b-2) in the aromatic group-containing (meth) acrylate-based macromer has an affinity with the pigment. From the viewpoint of increasing the amount, it is preferably 50% by weight or more, more preferably 70% by weight or more.

(B) The macromer may have a side chain composed of another structural unit such as an organopolysiloxane. This side chain can be obtained, for example, by copolymerizing a silicone macromer having a polymerizable functional group at one end represented by the following formula (1).
_{CH 2 = C (CH 3)} -COOC 3 H 6 - [Si (CH _{3) 2} O] _{t -Si (CH 3) 3 (} 1)
(In the formula, t represents a number of 8 to 40.)
Examples of commercially available styrenic macromers as component (b) include Toa Gosei Co., Ltd. trade names, AS-6 (S), AN-6 (S), HS-6 (S), and the like. It is done.

(C) The hydrophobic monomer is used from the viewpoint of improving the printing density and scratch resistance. Examples of the hydrophobic monomer include alkyl (meth) acrylate (c-1) and aromatic group-containing monomer (c-2).
As alkyl (meth) acrylate (c-1), what has a C1-C22, preferably C6-C18 alkyl group is preferable, for example, methyl (meth) acrylate, ethyl (meth) acrylate, ( Iso) propyl (meth) acrylate, (iso or tertiary) butyl (meth) acrylate, (iso) amyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, (iso) octyl (meth) Examples include acrylate, (iso) decyl (meth) acrylate, (iso) dodecyl (meth) acrylate, and (iso) stearyl (meth) acrylate.
In the present specification, “(iso or tertiary)” and “(iso)” mean both the case where these groups are present and the case where these groups are not present. Indicates. “(Meth) acrylate” refers to acrylate or methacrylate.

As the aromatic group-containing monomer (c-2), a vinyl monomer having an aromatic group having 6 to 22 carbon atoms, preferably 6 to 12 carbon atoms, which may have a substituent containing a hetero atom is preferable. Examples thereof include the styrene monomer (b-1) and the aromatic group-containing (meth) acrylate (b-2). Examples of the substituent containing a hetero atom include the same as those in the component (b-2).
As the styrene monomer (b-1), styrene or 2-methylstyrene is particularly preferable. (C) The content of the component (b-1) in the hydrophobic monomer is preferably 10 to 100% by weight, more preferably 20 to 80% by weight, from the viewpoint of improving scratch resistance.
As the aromatic group-containing (meth) acrylate (b-2), benzyl (meth) acrylate, phenoxyethyl (meth) acrylate and the like are particularly preferable. (C) The content of the component (b-2) in the hydrophobic monomer is preferably 10 to 100% by weight, more preferably 20 to 80% by weight from the viewpoint of improving scratch resistance. Moreover, it is also preferable to use (b-1) component and (b-2) component together.

The monomer mixture may further contain (d) a hydroxyl group-containing monomer (hereinafter sometimes referred to as “component (d)”). (D) The hydroxyl group-containing monomer has an excellent effect of enhancing the dispersion stability of the water-based ink.
As the component (d), for example, 2-hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, polyethylene glycol (n = 2 to 30, n represents the average number of added moles of oxyalkylene group. The same)) (meth) acrylate, polypropylene glycol (n = 2-30) (meth) acrylate, poly (ethylene glycol (n = 1-15) / propylene glycol (n = 1-15)) (meth) acrylate, etc. Can be mentioned. Among these, 2-hydroxyethyl (meth) acrylate, polyethylene glycol monomethacrylate, and polypropylene glycol methacrylate are preferable.

The monomer mixture further contains (e) a monomer represented by the following formula (2) (hereinafter also referred to as “(e) component”) from the viewpoint of improving the dispersion stability of the water-based ink. Also good.
^{_{CH 2 = C (R 1)}} COO (R 2 O) p R 3 (2)
Wherein R ¹ is a hydrogen atom or a lower alkyl group having 1 to 5 carbon atoms, R ² is a divalent hydrocarbon group having 1 to 30 carbon atoms which may have a hetero atom, and R ³ is , A monovalent hydrocarbon group having 1 to 30 carbon atoms which may have a hetero atom, p means an average added mole number, and represents a number of 1 to 60, preferably 1 to 30. )

In the formula (2), examples of the hetero atom that each of R ² and R ³ may have include a nitrogen atom, an oxygen atom, a halogen atom, and a sulfur atom.
Examples of the lower alkyl group having 1 to 5 carbon atoms represented by R ¹ include a methyl group, an ethyl group, and an (iso) propyl group.
As the R ² O group, an oxyethylene group, an oxy (iso) propylene group, an oxytetramethylene group, an oxyheptamethylene group, an oxyhexamethylene group, or a combination of one or more of these oxyalkylenes having 2 to 7 carbon atoms An oxyalkylene group etc. are mentioned.
The R ³ group includes an aliphatic alkyl group having 1 to 30 carbon atoms, preferably 1 to 20 carbon atoms, an alkyl group having 7 to 30 carbon atoms having an aromatic ring, and an alkyl having 4 to 30 carbon atoms having a heterocycle. Groups and the like.

  Specific examples of the component (e) include methoxypolyethylene glycol (1 to 30: the value of p in the formula (2). The same applies hereinafter) (meth) acrylate, methoxypolytetramethylene glycol (1 to 30) ( (Meth) acrylate, ethoxy polyethylene glycol (1-30) (meth) acrylate, octoxy polyethylene glycol (1-30) (meth) acrylate, polyethylene glycol (1-30) (meth) acrylate 2-ethylhexyl ether, (iso) Propoxy polyethylene glycol (1-30) (meth) acrylate, butoxy polyethylene glycol (1-30) (meth) acrylate, phenoxy polyethylene glycol (1-30) (meth) acrylate, methoxypolypropylene glycol (1-30) (meta Acrylate, phenoxyethyl polypropylene glycol (1-30) (meth) acrylate, methoxy (ethylene glycol-propylene glycol copolymer) (1-30, ethylene glycol therein: 1-29) (meth) acrylate. Among these, octoxy polyethylene glycol (1-30) (meth) acrylate, polyethylene glycol (1-30) (meth) acrylate 2-ethylhexyl ether, phenoxy polypropylene glycol (1-30) polyethylene glycol (1-30) (Meth) acrylate is preferred.

Specific examples of commercially available (d) and (e) components include Shin-Nakamura Chemical Co., Ltd. polyfunctional acrylate monomer (NK ester) M-40G, 90G, 230G, and Nippon Oil & Fats Co., Ltd. BLEMMER series, PE-90, 200, 350, PME-100, 200, 400, 1000, PP-500, 800, 1000, AP-150, 400, 550, 800 , 50PEP-300, 50POEP-800C and the like.
The above components (a) to (e) can be used alone or in combination of two or more.

The content of the components (a) to (e) in the monomer mixture at the time of producing the water-insoluble vinyl polymer (content as an unneutralized amount; the same shall apply hereinafter) or (a) to (e) in the water-insoluble polymer. ) The content of the structural unit derived from the component is preferably as follows.
The content of component (a) is preferably 3 to 30% by weight, more preferably 4 to 20% by weight, from the viewpoint of dispersion stability of the resulting dispersion.
The content of the component (b) is preferably 1 to 25% by weight, more preferably 5 to 20% by weight, particularly from the viewpoint of dispersion stability and scratch resistance of the polymer particles containing the pigment.
The content of the component (c) is preferably 10 to 70% by weight, more preferably 15 to 60% by weight, from the viewpoint of printing density and scratch resistance.
The content of component (d) is preferably 5 to 40% by weight, more preferably 7 to 20% by weight, from the viewpoint of dispersion stability.
The content of component (e) is preferably 5 to 50% by weight, more preferably 10 to 40% by weight, from the viewpoint of dispersion stability.

The total content of [(a) component + (d) component] in the monomer mixture is preferably 6 to 60% by weight, more preferably 10 to 50% by weight, from the viewpoint of dispersion stability in water. . The total content of [component (a) + component (e)] is preferably 6 to 75% by weight, more preferably 13 to 50% by weight, from the viewpoint of dispersion stability in water. The total content of [component (a) + component (d) + component (e)] is preferably 6 to 60% by weight, more preferably 7 to 50% by weight, from the viewpoint of dispersion stability in water. .
Further, the weight ratio of [(a) component / [(b) component + (c) component]] is preferably 0.01 to 1, more preferably 0.02 from the viewpoint of the dispersion stability obtained. It is 0.67, More preferably, it is 0.03-0.50.

The water-insoluble polymer used in the present invention can be produced by copolymerizing a monomer mixture by a known polymerization method such as a bulk polymerization method, a solution polymerization method, a suspension polymerization method or an emulsion polymerization method. Among these polymerization methods, the solution polymerization method is preferable.
The solvent used in the solution polymerization method is not particularly limited, but a polar organic solvent is preferable. When the polar organic solvent is miscible with water, it can be used by mixing with water. Examples of the polar organic solvent include aliphatic alcohols having 1 to 3 carbon atoms such as methanol, ethanol and propanol; ketones such as acetone and methyl ethyl ketone; esters such as ethyl acetate and the like. Among these, methanol, ethanol, acetone, methyl ethyl ketone, or a mixed solvent of one or more of these and water is preferable.

In the polymerization, azo compounds such as 2,2′-azobisisobutyronitrile, 2,2′-azobis (2,4-dimethylvaleronitrile), t-butyl peroxyoctate, dibenzoyl oxide, etc. Known radical polymerization initiators such as organic peroxides can be used.
The amount of the radical polymerization initiator used is preferably 0.001 to 5 mol, more preferably 0.01 to 2 mol, per mol of the monomer mixture.
In the polymerization, a known polymerization chain transfer agent such as mercaptans such as octyl mercaptan and 2-mercaptoethanol and thiuram disulfide may be further added.

Although the polymerization conditions of the monomer mixture vary depending on the type of radical polymerization initiator, monomer, solvent, etc. to be used and cannot be determined unconditionally, the polymerization temperature is usually preferably 30 to 100 ° C., more preferably 50 The polymerization time is preferably 1 to 20 hours. The polymerization atmosphere is preferably a nitrogen gas atmosphere or an inert gas atmosphere such as argon.
After completion of the polymerization reaction, the produced polymer can be isolated from the reaction solution by a known method such as reprecipitation or solvent distillation. Further, the obtained polymer can be purified by repeating reprecipitation or by removing unreacted monomers and the like by membrane separation, chromatographic method, extraction method and the like.

The weight average molecular weight of the water-insoluble polymer used in the present invention is preferably from 5,000 to 500,000, more preferably from 10,000 to 400,000, from the viewpoint of pigment dispersion stability, and from 10,000 to 300,000. Is more preferable.
The weight average molecular weight of the water-insoluble polymer is measured using polystyrene as a standard substance by gel chromatography using 60 mmol / L phosphoric acid and 50 mmol / L lithium bromide-containing dimethylformamide as a solvent.

  When the vinyl polymer used in the present invention has (a) a salt-forming group derived from a salt-forming group-containing monomer, it is neutralized with a neutralizing agent. As the neutralizing agent, an acid or a base can be used depending on the type of the salt-forming group in the polymer. For example, hydrochloric acid, acetic acid, propionic acid, phosphoric acid, sulfuric acid, lactic acid, succinic acid, glycolic acid, gluconic acid, glyceric acid and other acids, lithium hydroxide, sodium hydroxide, potassium hydroxide, ammonia, methylamine, dimethylamine , Bases such as trimethylamine, ethylamine, diethylamine, trimethylamine, triethanolamine, and tributylamine.

The degree of neutralization of the salt-forming group is preferably 10 to 200%, more preferably 20 to 150%, and particularly preferably 50 to 150%.
Here, the degree of neutralization can be determined by the following formula when the salt-forming group is an anionic group.
{[Weight of neutralizing agent (g) / equivalent of neutralizing agent] / [acid value of polymer (KOH mg / g) × polymer weight (g) / (56 × 1000)]} × 100
On the other hand, when the salt-forming group is a cationic group, it can be obtained by the following formula.
{[Weight of neutralizing agent (g) / equivalent of neutralizing agent] / [amine value of polymer (HCL mg / g) × polymer weight (g) / (36.5 × 1000)]} × 100
The acid value and amine value can be calculated from the structural unit of the polymer. Alternatively, it can also be determined by a method in which a polymer is dissolved in an appropriate solvent (for example, methyl ethyl ketone) and titrated.

In aqueous ink for ink jet recording of the manufacturing method of the present invention dispersions of water-insoluble polymer particles containing a yellow pigment, method for producing the dispersion of the water-insoluble polymer particles containing a yellow pigment is not particularly limited, for example, It can manufacture suitably by the method containing the following process (1) and process (2).
Step (1): Step of dispersing a mixture containing a water-insoluble polymer, an organic solvent, a yellow pigment, and water Step (2): Step of removing the organic solvent from the dispersion obtained in Step (1)

In step (1), first, the water-insoluble polymer is dissolved in an organic solvent, and then a yellow pigment, water, and, if necessary, a neutralizing agent, a surfactant and the like are added to the organic solvent and mixed. preferable. In the mixture, the yellow pigment content is preferably 5 to 50% by weight, more preferably 7 to 30% by weight, and the organic solvent content is preferably 5 to 70% by weight, more preferably 8 to 30% by weight. Preferably, the content of the water-insoluble polymer is preferably 1 to 40% by weight, more preferably 2 to 15% by weight, and the water content is preferably 10 to 80% by weight, more preferably 20 to 70% by weight. preferable.
When the water-insoluble polymer has a salt-forming group, it is preferable to use a neutralizing agent, but the degree of neutralization is not particularly limited. Usually, it is preferable that the liquid dispersion of the finally obtained water dispersion is neutral, for example, pH is 4.5 to 10. The pH can also be determined by the desired degree of neutralization of the water-insoluble polymer. Examples of the neutralizing agent include those described above. A water-insoluble polymer to be mixed may be appropriately neutralized with a neutralizing agent in advance.

  Examples of the organic solvent include alcohol solvents such as ethanol, isopropanol and isobutanol, ketone solvents such as acetone, methyl ethyl ketone and diethyl ketone, and ether solvents such as dibutyl ether, tetrahydrofuran and dioxane. Preferably, the solubility in water is 20% by weight or less and 20% by weight or more at 20 ° C. Among them, methyl ethyl ketone is preferred.

There is no restriction | limiting in particular about the method of carrying out the dispersion process of the mixture in the said process (1). In the present invention, the average particle diameter of the polymer particles can be atomized only by the main dispersion until the desired particle diameter is reached, but after the preliminary dispersion, the main dispersion is further performed by applying a shear stress to the polymer particles. It is preferable to control the average particle diameter of the particles so as to have a desired value.
Examples of means for applying the shear stress of this dispersion include a kneader such as a roll mill, a kneader and an extruder, a disperser such as a sand mill and a bead mill, and a chamber type high-pressure homogenizer. Among these, from the viewpoint of reducing the number of polymer particles having a particle diameter of 0.57 μm or more among water-insoluble polymer particles containing a pigment in water-based ink, a method of wet pulverization with a disperser using a dispersion medium Is preferred. Further, if necessary, a method of wet pulverization and then dispersing with a high-pressure homogenizer can be employed.

The material of the dispersion medium is preferably ceramic beads such as titania (TiO ₂ ), zirconia (ZrO ₂ ), zircon (ZrSiO ₄ ) alumina (Al ₂ O ₃ ) from the viewpoint of hardness, etc., and titania (TiO ₂ ), zirconia. (ZrO ₂ ) is more preferable.
The particle size of the dispersion medium is usually 50 to 500 μm, preferably 80 to 400 μm, from the viewpoint of efficiently reducing the number of polymer particles having a particle size of 0.57 μm or more.
In the wet pulverization dispersion, the weight ratio of the dispersion medium / dispersion liquid (including all dispersions such as organic pigment, polymer, water, organic solvent, etc.) is the viewpoint of reducing the number of polymer particles having a particle diameter of 0.57 μm or more Therefore, it is usually 10/1 to 4/6, preferably 10/1 to 5/5.

The peripheral speed of the disperser using the dispersion medium is the speed of the outer periphery of the stirring blade when it has a stirring blade. In the present invention, it is preferably 3 to 30 m / sec, more preferably 5 to 25 m / sec. It is. When there is no stirring blade, it is the rotational speed of the container, and in the present invention, it is preferably a speed of 0.1 to 1 m / sec.
The dispersion time is preferably 1 to 15 hours, and more preferably 2 to 10 hours, from the viewpoint of reducing the number of polymer particles having a particle size of 0.57 μm or more. From the same point, the temperature during dispersion is preferably 0 to 60 ° C, more preferably 5 to 30 ° C.

  In the step (2), an aqueous dispersion of polymer particles containing a yellow pigment can be obtained by distilling the organic solvent from the obtained dispersion by a known method to form an aqueous system. The organic solvent in the aqueous dispersion containing the obtained polymer particles is substantially removed, and the amount of the organic solvent is preferably 0.1% by weight or less, more preferably 0.01% by weight or less. Further, from the viewpoint of reducing the number of polymer particles having a particle diameter of 0.57 μm or more among water-insoluble polymer particles containing a pigment in the water-based ink, the aqueous dispersion can be separated by centrifugation. .

  In the present invention, the aqueous dispersion of water-insoluble polymer particles containing a yellow pigment refers to a dispersion in which a solid content of a polymer containing a yellow pigment is dispersed in a solvent containing water as a main solvent. Here, the form of the water-insoluble polymer particles is not particularly limited as long as the particles are formed of at least a yellow pigment and a water-insoluble polymer. For example, the particle form in which the yellow pigment is included in the polymer, the particle form in which the yellow pigment is uniformly dispersed in the polymer, the particle form in which the yellow pigment is exposed on the polymer particle surface, and the like are all included. The content ratio [(yellow pigment / water-insoluble polymer) weight ratio] of the yellow pigment to the water-insoluble polymer in the water-insoluble polymer particles containing the yellow pigment is 80/20 from the viewpoint of excellent scratch resistance and dispersion stability. 10/90, preferably 78/22 to 10/90, more preferably 75/25 to 50/50, and still more preferably 70/30 to 50/50.

(Ii) Yellow pigment dispersion dispersed with a water-soluble polymer
The “water-soluble polymer” used in the water-soluble polymer pigment dispersion means a polymer having a solubility in 100 g of water at 25 ° C. of 1 g or more, preferably 10 g or more, more preferably 50 g or more. The amount of dissolution means the solubility after 100% neutralization with sodium hydroxide or acetic acid depending on the salt-forming group, if it has a salt-forming group.
The neutralization degree of the water-soluble polymer is preferably 50 to 150% from the viewpoint of the dispersion stability of the pigment dispersion. The degree of neutralization can be determined by the above formula.
What is necessary is just to select suitably as a neutralizing agent used in the case of neutralization according to the kind of salt formation group of a water-soluble polymer. For example, when the water-soluble polymer is obtained from a cationic monomer, acetic acid, methoxyacetic acid, propionic acid, lactic acid, succinic acid, glycolic acid, gluconic acid, glyceric acid, etc. may be used as a neutralizing agent. it can. Further, when the water-soluble polymer is obtained from an anionic monomer, as a neutralizing agent, tertiary amines such as trimethylamine and triethylamine, sodium hydroxide, potassium hydroxide, lithium hydroxide, ammonia and the like are used. Can be used.

As the water-soluble polymer, for example, a water-soluble vinyl polymer, a water-soluble ester polymer, a water-soluble urethane polymer and the like can be used. Of these polymers, water-soluble vinyl polymers are preferred.
Examples of the water-soluble vinyl polymer include a copolymer obtained by polymerizing a monomer composition containing (a) a salt-forming group-containing monomer and (b) a hydrophobic monomer. In addition, this monomer composition may contain (c) nonionic hydrophilic monomer as needed.
As each of (a) a salt-forming group-containing monomer, (b) a hydrophobic monomer, and (c) a nonionic hydrophilic monomer, (a) component, (b) component used for the water-insoluble vinyl polymer, (C) The thing similar to a component is mentioned.

The content of (a) a salt-forming group-containing monomer, (b) a hydrophobic monomer, and (c) a nonionic hydrophilic monomer in the monomer composition that is a raw material of the water-soluble polymer, or these monomers in the water-soluble polymer The content of the structural unit derived from is not particularly limited as long as the water-soluble polymer is soluble in water after its neutralization, and is excellent in the dispersion stability of the pigment in the ink and the discharge property of the ink. Usually, the content of the monomer (a) containing a salt-forming group is 30 to 90% by weight, preferably 30 to 70% by weight.
(B) Content of hydrophobic monomer is 10 to 70% by weight, preferably 30 to 70% by weight.
(C) The content of the nonionic hydrophilic monomer is 0 to 75% by weight, preferably 1 to 60% by weight.
The total content of (a) the salt-forming group-containing monomer and (c) the nonionic hydrophilic monomer in the monomer composition is 30 to 80% by weight, preferably 30 to 70% by weight.

  In the present invention, the content is as follows: (a) 30 to 90% by weight of a salt-forming group-containing monomer, (b) 10 to 70% by weight of a hydrophobic monomer, and (c) 0 to 75% by weight of a nonionic hydrophilic monomer. The total content of (a) the salt-forming group-containing monomer and (c) the nonionic hydrophilic monomer in the monomer composition is preferably 30 to 80% by weight. The monomer composition contains (a) 30 to 70% by weight of a salt-forming group-containing monomer, (b) 30 to 70% by weight of a hydrophobic monomer, and (c) 1 to 60% by weight of a nonionic hydrophilic monomer, and More preferably, the total content of (a) the salt-forming group-containing monomer and (c) the nonionic hydrophilic monomer in the monomer composition is 30 to 70% by weight.

The weight average molecular weight of the water-soluble polymer is 500 to 30,000, preferably 800 to 20,000, more preferably 1,000 to 10,000 in consideration of the dispersion stability of the pigment in the ink and the ink viscosity. It is desirable. The weight average molecular weight of the water-soluble polymer can be measured by the same method as in the case of the water-insoluble polymer.
The content of the water-soluble polymer in the dispersion is preferably from 5 to 100 parts by weight, more preferably from 7 to 100 parts by weight, based on 100 parts by weight of the yellow pigment, from the viewpoint of the dispersion stability of the pigment in the ink and the ink ejection properties. 80 parts by weight, more preferably 10 to 60 parts by weight. The water-soluble polymer used in the present invention can be produced by copolymerizing a monomer mixture by a known polymerization method.

The dispersion in which the yellow pigment is dispersed with the water-soluble polymer may further contain a pigment derivative, a surfactant and the like.
Examples of pigment derivatives include ionic functional groups or salts of ionic functional groups, azo derivatives, diazo derivatives, phthalocyanine derivatives, quinacridone derivatives, isoindolinone derivatives, dioxazine derivatives, perylene derivatives, perinone derivatives, thioindigo derivatives, And anthraquinone derivatives and quinophthalone derivatives.

Examples of the surfactant include anionic, cationic, nonionic and amphoteric surfactants. Among these, anionic surfactants are preferable from the viewpoints of dispersion stability and dischargeability. More specifically, a sodium salt of β-naphthalenesulfonic acid-formalin condensate (for example, Kao Corporation, trade names: Demol N, Demol RN, Demol MS, etc.), polycarboxylic acid type polymer surfactant [ For example, product name: Poise 520, Poise 521, Poise 530, etc. manufactured by Kao Corporation] is preferable.
The amount of the surfactant and the pigment derivative is preferably 1 to 120 parts by weight, more preferably 3 to 100 parts by weight with respect to 100 parts by weight of the yellow pigment, from the viewpoints of the dispersion stability of the pigment in the ink and the discharge property of the ink. 70 parts by weight, more preferably 5 to 30 parts by weight.

Method for producing dispersion in which yellow pigment is dispersed with water-soluble polymer The method for producing a dispersion in which yellow pigment is dispersed in water-soluble polymer is not particularly limited. Water-soluble polymer, yellow pigment, water, and as necessary Accordingly, it can be obtained by mixing a neutralizing agent. In the above mixture, the yellow pigment content is preferably 3 to 30% by weight, the water-soluble polymer content is preferably 1 to 30% by weight, and the water content is preferably 40 to 80% by weight.

Furthermore, if necessary, from the viewpoint of reducing the number of dispersions having a particle diameter of 0.57 μm or more among the dispersions in which the yellow pigment in the water-based ink is dispersed, the above-mentioned water-insoluble polymer is used for dispersion. The dispersion method used at the time, that is, a dispersion method using a kneading machine such as a roll mill, a kneader or an extruder, a dispersion machine such as a sand mill or a bead mill, a chamber type high-pressure homogenizer, or the like can be used.
Further, from the viewpoint of reducing the number of dispersions having a particle diameter of 0.57 μm or more among the dispersions in which the yellow pigment is dispersed in the water-based ink, the dispersion can be separated by centrifugation.

[Water-based ink for inkjet recording]
The content of each component in the water-based ink for ink-jet recording of the present invention and the ratio thereof are as follows.
From the viewpoint of printing density and scratch resistance, the content of each of the water-insoluble polymer particles in the case of using the water-insoluble polymer or the water-insoluble polymer in the case of using the dispersion dispersed in the water-soluble polymer is Preferably it is 0.5 to 15 weight%, More preferably, it is 0.7 to 10 weight%, More preferably, it is 1 to 8 weight%.
The content of the yellow pigment is 4.5% by weight or more, preferably 5.0% by weight or more, more preferably 5.5% by weight or more, from the viewpoint of increasing the dispersion stability and the print density. From the viewpoint of properties, it is preferably 15% by weight or less, and more preferably 10% by weight or less.

The average particle diameter of the yellow pigment dispersion in the obtained water-based ink is preferably 0.03 to 0.25 μm, more preferably 0.05 to 0, from the viewpoint of preventing clogging of the printer nozzle and scratch resistance. .2 μm, particularly preferably 0.07 to 0.15 μm. The average particle diameter can be measured using a light scattering method using laser light. Specifically, the average particle diameter is measured under the following conditions using a laser particle analysis system ELS-8000 (cumulant analysis) manufactured by Otsuka Electronics Co., Ltd. can do.
Temperature: 25 ° C
Angle between incident light and detector: 90 °
Accumulation count: 100 times Refractive index of dispersion solvent: Enter the refractive index of water (1.333) Measurement concentration: Usually about 5 × 10 ^-3 wt%

  The ratio of the average particle diameter of the yellow pigment dispersion to the average primary particle diameter of the yellow pigment (the average particle diameter of the yellow pigment dispersion / the average primary particle diameter of the yellow pigment) is 1 from the viewpoint of scratch resistance, glossiness, and the like. 0.001 to 4 are preferable, and 1.01 to 3 are more preferable.

In the water-based ink for ink jet recording of the present invention, the number of polymer particles having a particle size of 0.57 μm or more out of the particle size of the yellow pigment dispersion is 1.2 × 10 ⁷ particles / ml or less from the viewpoint of scratch resistance. The water-based ink is preferably 1.0 × 10 ⁷ pieces / ml or less, more preferably 0.8 × 10 ⁷ pieces / ml or less.
The number of dispersions having a particle diameter of 0.57 μm or more can be measured using a single particle optical detection method (SPOS), and specifically, can be measured using an ACCUSIZER manufactured by PARTICLE SIZING SYSTEMS. As a measurement method, 0.5 ml of ink diluted to 5 ml with pure water is used, and the number of particles having a particle diameter of 0.57 μm or more contained in the ink can be measured at a measurement temperature of 25 ° C.

In the present invention, the water-based ink refers to an ink using water as a main solvent. The water content in the water-based ink of the present invention is preferably 30 to 90% by weight, more preferably 40 to 80% by weight. It is.
The dispersion may be used as a water-based ink as it is, but wetting agents, penetrants, dispersants, viscosity modifiers, antifoaming agents, antifungal agents, rust-proofing agents and the like that are usually used for water-based inks for inkjet recording are used. It may be added and used as a water-based ink.
The surface tension (20 ° C.) of the water-based ink for inkjet recording of the present invention is preferably 25 to 50 mN / m, and more preferably 27 to 45 mN / m.
The viscosity (20 ° C.) of the water-based ink for ink jet recording of the present invention is preferably 2 to 12 mPa · s, and more preferably 2.5 to 10 mPa · s, in order to maintain good discharge properties.

In the water-based ink for ink-jet recording of the present invention, the average particle diameter increase rate of the yellow pigment dispersion in the water-based ink after storage at 90 ° C. for 48 hours is 20% or less, and further 10% from the viewpoint of dispersion stability. The following is preferable. The average particle diameter increase rate can be expressed by the following equation, and the average particle diameter can be obtained by the above-described measuring method.
Average particle diameter increase rate (%) = [(average particle diameter of yellow pigment dispersion in aqueous ink after storage−average particle diameter of yellow pigment dispersion in aqueous ink before storage) / (aqueous ink before storage) Average particle size of yellow pigment dispersion in the inside)] × 100

  In the following production examples, examples and comparative examples, “parts” and “%” mean “parts by weight” and “% by weight” unless otherwise specified.

Production Example 1
In a reaction vessel, 20 parts of methyl ethyl ketone, 0.03 part of a polymerization chain transfer agent (2-mercaptoethanol), and 10% of 200 parts of the monomer mixture shown in Table 1 are mixed and mixed, and nitrogen gas replacement is sufficiently performed. And a mixed solution was obtained.
On the other hand, the remaining 90% of the monomer mixture shown in Table 1 was charged into a dropping funnel, and 0.17 part of the polymerization chain transfer agent, 60 parts of methyl ethyl ketone and a radical polymerization initiator (2,2′-azobis (2,4- Dimethylvaleronitrile)) 1.1 parts were added and mixed, and the gas was sufficiently replaced with nitrogen gas to obtain a mixed solution.
Under a nitrogen atmosphere, the mixed solution in the reaction vessel was heated to 65 ° C. while stirring, and the mixed solution in the dropping funnel was gradually dropped over 3 hours. After 2 hours at 65 ° C. from the end of dropping, a solution obtained by dissolving 0.3 part of the radical polymerization initiator in 5 parts of methyl ethyl ketone was added, and further aged at 65 ° C. for 2 hours and 70 ° C. for 2 hours to obtain a polymer solution. It was.
The weight average molecular weight of the obtained polymer was measured by the above method. The results are shown in Table 1.

The details of the compounds shown in Table 1 are as follows.
Styrene macromer: manufactured by Toa Gosei Co., Ltd., trade name: AS-6 (S) (50% toluene solution, solid content 50%) number average molecular weight: 6000, polymerizable functional group: methacryloyloxy group, polyethylene glycol monomethacrylate ( Ethylene oxide average added mole number = 9): Shin-Nakamura Chemical Co., Ltd., trade name: NK ester M-90G
Polypropylene glycol monomethacrylate (average number of added moles of propylene oxide = 9): manufactured by NOF Corporation, trade name: BLEMER PP-800

Example 1
22.5 parts of the polymer obtained by drying the polymer solution obtained in Production Example 1 under reduced pressure was dissolved in 70 parts of methyl ethyl ketone, and 4.6 parts of neutralizing agent (5N aqueous sodium hydroxide solution) was contained therein (degree of neutralization). 75%) and 230 parts of ion-exchanged water were added to neutralize the salt-forming group, and diazo pigment (yellow: Y) (CI Pigment Yellow 74 [PY 74], average primary particle size 40 nm) 77.5 parts, manufactured by Sanyo Dye Co., Ltd., trade name: FY7413), and added by using Asahi Iron Works Co., Ltd. Picomill (dispersion media: zirconia temperature: 20 ° C., dispersion media / dispersion ratio: 8/2) Dispersion treatment was performed for 4 hours at a speed of 12 m / s. The obtained mixture was subjected to 10-pass dispersion treatment at a pressure of 200 MPa with a microfluidizer (trade name, manufactured by Microfluidics).

After adding 250 parts of ion-exchanged water to the obtained dispersion and stirring, methyl ethyl ketone was removed at 60 ° C. under reduced pressure, a part of water was further removed, and a 5 μm filter (acetylcellulose membrane, outer diameter: A pigment-containing water-insoluble polymer having a solid content of 20% by filtering with a 25 mL needleless syringe (Terumo Corporation) attached with 2.5 cm, Fuji Photo Film Co., Ltd.), and removing coarse particles. An aqueous dispersion of particles was obtained.
To 40 parts of the aqueous dispersion of pigment-containing water-insoluble polymer particles, 10 parts of glycerin, 7 parts of triethylene glycol monobutyl ether, 1 part of Surfinol 465 (manufactured by Nissin Chemical Industry Co., Ltd.), Proxel XL2 (Abisia Corporation) 0.3 parts) and 41.7 parts of ion-exchanged water were mixed, and the obtained mixed solution was attached with a 1.2 μm filter (acetylcellulose membrane, outer diameter: 2.5 cm, manufactured by Fuji Photo Film Co., Ltd.). The aqueous ink 1 was obtained by filtering with a syringe with a needle of 25 mL and removing coarse particles.

Example 2
In Example 1, the aqueous system was changed in the same manner except that 40 parts of the aqueous dispersion of pigment-containing water-insoluble polymer particles was changed to 30 parts, 10 parts of glycerin to 15 parts, and 41.7 parts of ion-exchanged water to 46.7 parts. Ink 2 was obtained.

Example 3
35 parts of the polymer obtained by drying the polymer solution obtained in Production Example 1 under reduced pressure was dissolved in 100 parts of methyl ethyl ketone, and 7.2 parts of neutralizing agent (5N aqueous sodium hydroxide solution) was contained therein (degree of neutralization 75%). ) And 300 parts of ion-exchanged water were added to neutralize the salt-forming group, and diazo pigment (yellow: Y) (CI Pigment Yellow 74 [PY74], average primary particle size 40 nm, Sanyo 65 parts by Dye Co., Ltd., trade name: FY7413) was added, and dispersion treatment was performed for 2 hours at a peripheral speed of 15 m / s using Asako Tekko Picomill. The obtained mixture was subjected to 10-pass dispersion treatment at a pressure of 200 MPa with a microfluidizer (trade name, manufactured by Microfluidics). Thereafter, an aqueous ink 3 was obtained in the same manner as in Example 1.
Example 4
A water-based ink 4 was obtained in the same manner as in Example 3, except that 35 parts of the polymer was 20 parts, 7.2 parts of the neutralizing agent was 4.1 parts, and 65 parts of the diazo pigment was 80 parts.

Comparative Example 1
A water-based ink 5 was obtained in the same manner as in Example 1 except that the processing conditions at Asako Teiko Co., Ltd. Picomill were changed to a peripheral speed of 12 m / s and a processing time of 1 hour.
Comparative Example 2
In Example 1, the treatment conditions at Asako Teiko Co., Ltd. Picomill were changed to a peripheral speed of 12 m / s and a treatment time of 2 hours, and 40 parts of an aqueous dispersion of pigment-containing water-insoluble polymer particles were changed to 25 parts. A water-based ink 6 was obtained in the same manner except that the part was changed to 20 parts and the ion-exchanged water 41.7 parts to 46.7 parts.

Comparative Example 3
300 parts of ion-exchanged water is added to 40 parts of a water-soluble polymer (Joncryl, trade name HPD61J, effective content: 30.5%), and a diazo pigment (yellow: Y) (CI Pigment Yellow 74) is added thereto. [P.Y.74], average primary particle size 40 nm, Sanyo Dye Co., Ltd., trade name: FY7413) 60 parts were added, Asada Tekko Co., Ltd. Picomill (dispersion media: zirconia Temperature: 20 ° C., dispersion media / dispersion) Using a liquid ratio: 8/2), dispersion treatment was performed for 2 hours at a peripheral speed of 15 m / s. The obtained mixture was subjected to 10-pass dispersion treatment at a pressure of 200 MPa with a microfluidizer (trade name, manufactured by Microfluidics).
Ion exchange water was added to the resulting dispersion and stirred, and then a 25 mL needleless syringe (Terumo) attached with a 5 μm filter (acetylcellulose membrane, outer diameter: 2.5 cm, manufactured by Fuji Photo Film Co., Ltd.) The product was filtered through a product of Co., Ltd. and coarse particles were removed to obtain an aqueous dispersion of pigment-containing water-soluble polymer particles having a solid content concentration of 20%.

  In 40 parts of the aqueous dispersion of the pigment-containing water-soluble polymer particles, 10 parts of glycerin, 7 parts of triethylene glycol monobutyl ether, 1 part of Surfinol 465 (manufactured by Nissin Chemical Industry Co., Ltd.), Proxel XL2 (Avicia Co., Ltd.) 0.3 parts) and 41.7 parts of ion-exchanged water were mixed, and the obtained mixed solution was attached with a 1.2 μm filter (acetylcellulose membrane, outer diameter: 2.5 cm, manufactured by Fuji Photo Film Co., Ltd.). The aqueous ink 7 was obtained by filtering with a 25 mL needleless syringe and removing coarse particles.

For each of the water-based inks 1 to 7 obtained as described above, the average particle size of the polymer particles, the number of polymer particles having a particle size of 0.57 μm or more, scratch resistance, print density, and storage stability are obtained. It measured by the following method. The results are shown in Table 2.
(1) Average particle diameter: It was determined by cumulant analysis using ELS-8000 manufactured by Otsuka Electronics Co., Ltd. The measurement conditions were a temperature of 25 ° C., an angle between incident light and a detector of 90 °, and the number of integrations of 100 times.
(2) Number of polymer particles having a particle diameter of 0.57 μm or more: The number of polymer particles of 0.57 μm or more was measured using ACCUSIZER manufactured by PARTICLE SIZING SYSTEMS. As the measuring method, 0.5 ml of ink diluted to 5 ml with pure water was used, and the number of particles of 0.57 μm or more contained in the ink was measured (measurement temperature: 25 ° C.).

(3) Scratch resistance: using an ink jet printer (manufactured by Epson Corporation, model number: EM-930C), exclusive paper (photographic paper <gloss> (60 ° gloss is 41), manufactured by Epson Corporation, product (Name: KA450PSK) [printing conditions: paper type; photo print paper, mode setting; photo], dried at 25 ° C. for 24 hours, and then rubbed the print surface with a finger three times. The degree of disturbance of the printed surface at that time was evaluated based on the following evaluation criteria each time, and averaged to quantify the scratch resistance. An average value of 4.0 or more is practical for photography.
〔Evaluation criteria〕
5: Image distortion is not observed at all regardless of viewing angle 4: Disturbance is observed in a slight rubbing trace depending on the viewing angle 3: Disturbance is observed in the rubbing trace 2: Recognizing the rubbing trace clearly Yes, the image is very disturbed 1: Clearly the image is scratched

(4) Printing density (standard test): Using an inkjet printer (manufactured by Epson Corporation, model number: EM-930C), solid printing is performed on commercially available plain paper (manufactured by Seiko Epson Corporation, trade name: KA4250NP) [ Printing conditions: paper type; plain paper, mode setting; photo], left at 25 ° C. for 1 hour, and then measured the printing density with a Macbeth densitometer (manufactured by Macbeth, product number: RD914), and determined the average value. From the viewpoint of high printing density, 1.10 or more is preferable.
(5) Storage stability: 5 ml of ink was weighed into a 20 ml screw tube, sealed with a seal tape, and then left in a thermostatic bath set at 90 ° C. for 2 days (48 hours). The average particle diameter before and after the test was measured, and the increase rate was calculated. From the viewpoint of dispersion stability, the average particle size increase rate is preferably 20% or less, and more preferably 10% or less.

Claims (6)

A water-based ink containing a yellow pigment dispersion, the number of yellow pigment dispersions containing 4.5% by weight or more of the yellow pigment and having a particle diameter of 0.57 μm or more among the yellow pigment dispersions A water-based ink for ink-jet recording, wherein is 1.2 × 10 ⁷ pieces / ml or less.   The aqueous ink according to claim 1, wherein the yellow pigment dispersion has an average particle size of 0.03 to 0.25 μm.   The water-based ink according to claim 1 or 2, wherein the average particle size increase rate of the yellow pigment dispersion in the water-based ink after being stored at 90 ° C for 48 hours is 20% or less.   The yellow pigment is C.I. I. Pigment yellow 74 and C.I. I. The water-based ink according to claim 1, wherein the water-based ink is one or more selected from the group consisting of CI Pigment Yellow 97.   The water-based ink according to any one of claims 1 to 4, wherein the yellow pigment has an average primary particle diameter of 10 to 200 nm.   The water-based ink according to any one of claims 1 to 5, wherein the yellow pigment dispersion is a dispersion of a yellow pigment contained in water-insoluble polymer particles.